Recognition of extracellular ligands by cell surface receptors (integrins) is critical for cell adhesion, migration and tracking and perhaps the metastatic spread of tumor cells. This recognition is mediated in part by an arginine-glycine-aspartic acid sequence in extracellular proteins. We have recently cloned and expressed larger multimodule fragments that each contain the module FN 11110. We have crystallized three of these fragments. These fragments are important structural candidates to reveal the 3D organization of the RGD site and synergistic sites in adjacent domains that are required for integrin recognition and adhesive function of the molecules.